1. Field of the Invention
The present invention relates generally to sealing gaskets and sealing systems used for pipe joints in plastic pipelines in which a male spigot pipe section is installed within a mating female socket pipe section to form a pipe joint and, more specifically, to an improved gasket and installation method for installing a locked-in gasket within a preformed gasket groove in a section of pipe used to form a pipe joint.
2. Description of the Prior Art
Fluid sealing systems for plastic, fluid conveying pipes are used in a variety of industries. The pipes used in such systems are typically formed from thermoplastic materials including polyolefins and PVC. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. Various types of sealing technologies have been employed to assure the sealing integrity of the pipe joint. It is important that the sealing gasket not be dislodged during the joint make up and that the gasket not become twisted or otherwise compromised in field applications.
In earlier gasketed sealing systems, the gasket was generally deformable, allowing it to be flexed or bent by hand and inserted within a mating groove formed in the female, belled pipe end. One attempt to insure the integrity of such pipe joints involved the use of a pipe gasket having one region formed of an elastically yieldable sealing material, such as rubber, and a second distinct region formed of a more rigid material, such as a rigid plastic. The rigid region of the gasket tended to hold the gasket in place within the pipe groove. Other approaches to the problem included the use of a homogeneous rubber ring with a stiffening band which was manually inserted into a mating groove provided on the internal diameter of the rubber ring. In other words, the rubber ring was first flexed or bent and inserted into the groove in the belled pipe end. The rigid retaining ring was then inserted into a groove in the rubber gasket ring. Each of these solutions was less than ideal, in some cases failing to provide the needed joint integrity and often contributing to the complexity and expense of the manufacturing operation.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system employed a combined mould element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Rieber process, an elastomeric gasket was installed within an internal groove in the socket end of the female pipe as the female or belled end was simultaneously being formed. Rather than utilizing a preformed groove, the Rieber process provided a prestressed and anchored elastomeric gasket during the belling operation. Because the gasket was installed simultaneously with the formation of the belled pipe end, a rigid, embedded reinforcing ring could be supplied as a part of the gasket. Because the pipe groove was, in a sense, formed around the gasket with its embedded reinforcing ring, the gasket was securely retained in position and did not tend to twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
Despite the advances offered by the Rieber process, the belling operation was somewhat complicated and costly. Also, certain situations exist in which it would be desirable to install a gasket within a preformed groove in the selected pipe end, rather than utilizing an integrally installed gasket in which the groove in the pipe is formed around the gasket.
As mentioned above, in the prior art joints utilizing preformed grooves, gaskets were often provided in two parts. The main gasket body was formed of an elastomeric material and typically featured an internal groove or recess The main gasket body was first flexed by hand and installed within the groove provided in the belled pipe end. A hardened band, formed of rigid plastic or metal, was then installed by hand within the groove provided on the internal circumference of the gasket. While such retaining bands helped to resist axial forces acting on the gasket during assembly of the joint, the band could become displaced or twisted during the insertion operation. It would therefore be advantageous to be able to install a gasket of the type having an embedded reinforcing ring within a previously belled pipe end. However, gaskets with embedded reinforcing rings are not easily bent or flexed by hand, thus generally precluding hand assembly in the field. The size and position of the embedded ring within the gasket body generally was greater than the diameter of the mouth opening of the belled pipe end, presenting a further complication for assembly.
U.S. Pat. No. 6,044,539, issued Apr. 4, 2000, to Guzowski, and commonly owned by the present applicant describes a machine for inserting a “snap-fit” gasket having an embedded reinforcing ring into a preformed gasket receiving groove in a belled pipe end. However, such a machine was fairly costly to construct and was not capable of being hand carried by a worker in the field.
The present invention has, as one object, to provide an improved pipe gasket for use in pipe joints which offers the advantage of a Rieber type locked-in seal while allowing the gasket to be installed in a preformed groove in snap-fit fashion, either at the manufacturing plant or in a field operation.
Another object of the invention is to provide an improved gasket which is securely retained within a preformed pipe groove without the necessity of a separate retaining band.
Another object of the invention is to provide an improved method of installing a reinforced gasket within a preformed pipe groove.
Another object of the invention is to provide a method for installing a gasket having a known external diameter within the mouth opening of a belled end of a pipe section where the external diameter of the gasket exceeds the internal diameter of the mouth opening of the pipe section.
Another object of the invention is to provide an improved gasket installation apparatus which is simpler and less costly than existing devices and installation techniques.